Coloured matter removal from sugar-beet industry syrup by ultra- and nanofiltration

Abstract

The produced sugar, as the final product in sugar production technology, has to contain as low non-sucrose compounds with coloured matters as possible. Ultrafiltration and nanofiltration could be one of the solutions for a more effective separation of non-sucrose compounds from intermediate products from which sucrose directly crystallises. The separation of non-sucrose compounds by ultra- and nanofiltration is investigated on syrup solution with 40% d.m. content, which is an intermediate product in the phase of sucrose crystallisation. Further, this paper investigates variables in the ultrafiltration and nanofiltration of syrup solutions, such as variations in pore sizes of the polymer membranes, syrup temperatures, syrup flow rates and transmembrane pressures. During ultrafiltration, under the investigated conditions; permeate flux is about 10 times less than water flux (150 l m -2h-1) on the first membrane and 8 times less than water flux (285 l m-2h-1) on the second membrane, while the nanofiltration permeate flux is 15 times less than water flux (320 l m -2h-1). The permeate flux decreases due to the adsorption of non-sucrose compounds by the filter membranes and the resultant increase in resistance to mass transfer. The colour content is about 58% lower by ultrafiltration using membranes. There is no great difference in colour separation between the used ultrafiltration membranes with different pore sizes. Nanofiltration was shown to separate 76% of coloured matter from syrup. In all the examined cases, permeate turbidity could be reduced by 75-80%, according to feed.